1. Field of the Invention
The present invention relates to a device and module of triggering and generating temperature coefficient current, and more particularly, to a device and module of triggering and generating temperature coefficient current capable of utilizing current canceling effect to smooth temperature coefficient current with simple circuit during state switching around a triggering temperature.
2. Description of the Prior Art
Because of characteristics of semiconductors, an output current of a current source is designed to be with temperature coefficient, i.e. the output current varies with environment temperature, among many applications, so as to compensate a temperature effect due to non-ideal factors of different circuits.
For example, please refer to FIG. 1, which is a schematic diagram of a conventional dual capacitor oscillator 10. In short, an ideal oscillating frequency fideal of the dual capacitor oscillator 10 can be denoted as
            f      ideal        =                  I        c                    2        ⁢                  C          f                ⁢                  V          ref                      ,which means a current Ic provided from a current source determines the ideal oscillating frequency fideal. However, the ideal oscillating frequency fideal is influenced by temperature due to non-ideal effects of the dual capacitor oscillator 10, and thus after summing every critical factor the relation between temperature and frequency, i.e. temperature coefficient, is non-linear, and frequency varies significantly within a specific temperature range. In such a situation, a current source designer must take the non-linear temperature coefficient into consideration, such that the current Ic provided to the dual capacitor oscillator 10 compensates a frequency shift of the dual capacitor oscillator 10. In other words, if the frequency increases as temperature increases within a specific temperature range after summing different influencing factors, there is a need to design a current Ic decreases as temperature increases within the specific temperature range to offset frequency shift causing by the influencing factors.
Please refer to FIG. 2, which is a schematic diagram of a conventional current source 20 with non-linear temperature coefficient. As shown in FIG. 2, the current source 20 includes a conventional energy bandgap reference circuit 202, a triggering unit 204 and a generating unit 206. In short, the conventional energy bandgap reference circuit 202 provides voltages and currents with or without temperature coefficients to the triggering unit 204, and thus the triggering unit 204 triggers to control the switch generating unit 206 to output in some specific temperature conditions, such that the generating unit 206 outputs an output current Iout with temperature coefficient.
For example, the conventional energy bandgap reference circuit 202 provides a voltage VZTC with zero temperature coefficient to a positive input terminal of a comparator 208 of the triggering unit 204. And the triggering unit 204 generates a current IPTC with positive temperature coefficient via a transistor M1 of a current mirror, such that the current IPTC with positive temperature coefficient flows through a resistor RPTC, and is transferred into a voltage VPTC with positive temperature coefficient to a negative input terminal of the comparator 208. The comparator 208 compares the voltage VPTC with zero temperature coefficient with the voltage VPTC with positive temperature coefficient, so as to output a control signal Vcon to control the switch generating unit 206 to output. Method of the conventional energy bandgap reference circuit 202 providing the voltage VZTC with zero temperature coefficient and the current IPTC with positive temperature coefficient is well known by those skilled in the art, and is not narrated hereinafter.
Besides, in the generating unit 206, an amplifier 210 is arranged to utilize feedback to lock a voltage of a positive input terminal of the amplifier 210 in the zero temperature coefficient voltage VZTC, which means when the voltage of the positive input terminal of the amplifier 210 is less than the voltage VZTC with zero temperature coefficient, a transistor M2 is turned on to pull the voltage of the positive input terminal of the amplifier 210 high. Thus, the generating unit 206 can generate a zero temperature coefficient current IZTC flowing through a resistor RZTC, and then a transistor M3 of a current mirror is utilized for generating the current IZTC with zero temperature coefficient to a high voltage level input terminal of a multiplexer 212. On the other hand, a transistor M4 of another current mirror is utilized for generating the positive temperature coefficient current IPTC to a low voltage input terminal of the multiplexer 212. And then, the multiplexer 212 switches to output the zero temperature coefficient current IZTC and the positive temperature coefficient current IPTC according to the control signal Vcon.
Noticeably, the example shown in FIG. 2 is designed that the zero temperature coefficient voltage VZTC equals the positive temperature coefficient voltage VPTC when the environment temperature is a triggering temperature Ttrigger. In such a situation, please refer to FIG. 3, which is a schematic diagram of the output current Iout, the zero temperature coefficient current IZTC and the positive temperature coefficient current IPTC shown in FIG. 2 under an ideal condition. As shown in FIG. 2 and FIG. 3, when the environment temperature is lower than the triggering temperature Ttrigger, the comparator 208 outputs the control signal Vcon at a high voltage level, such that the multiplexer 212 selects the zero temperature coefficient current IZTC as the output current Iout. When the environment temperature increases, the positive temperature coefficient voltage VPTC increases accordingly; when the environment temperature is higher than the triggering temperature Ttrigger, the positive temperature coefficient voltage VPTC is greater than the zero temperature coefficient voltage VZTC, such that the control signal Vcon outputted by the comparator 208 is switched to a low voltage level, and thus the multiplexer 212 selects the positive temperature coefficient current IPTC as the output current Iout. As a result, the output current Iout has zero temperature coefficient when the environment temperature is lower than the triggering temperature Ttrigger; and when the environment temperature is higher than the triggering temperature Ttrigger, the output current Iout has the positive temperature coefficient to cancel the negative temperature coefficient in the circuit, and thus the output current Iout has a non-linear temperature coefficient within a whole temperature range.
However, the current source 20 utilizes the comparator 208 to compare voltages to determine temperature and then decides the output current Iout accordingly. In such a situation, the circuit structure is more complicated, i.e. a basic structure of the comparator 208 requires at least 5 transistors for making a simple operation amplifier, and such a method of digital switching may have current discontinuity due to some manufacturing process factors. As shown in FIG. 3, the output current Iout forms a turning point of current to temperature at the triggering temperature Ttrigger, and the zero temperature coefficient current IZTC and the positive temperature coefficient current IPTC must be the same Itrigger at the turning point. If the zero temperature coefficient current IZTC and the positive temperature coefficient current IPTC are not matched at triggering the temperature Ttrigger due to manufacturing process drift, the output current Iout appears discontinuous when the environment temperature across the turning point due to digital switching.
For example, please refer to FIG. 4, which is a schematic diagram of the output current Iout, the zero temperature coefficient current IZTC and the positive temperature coefficient current IPTC shown in FIG. 2 under a non-ideal condition. As shown in FIG. 4, if the positive temperature coefficient current IPTC does not equal the zero temperature coefficient current IZTC at the triggering temperature Ttrigger due to manufacturing process drift, the output current Iout may be discontinuous.
In addition, it is difficult for the conventional structure to provide a current with temperature coefficient including multiple turning points, and the temperature coefficients before and after a turning point change greatly due to output state switching of the comparator 208, i.e. digital operation, which is difficult to adjust arbitrarily and increases layout area and power consumption for compensating different temperatures. Besides, if the traditional energy bandgap reference circuit 202 tends to generate the negative temperature coefficient current, a resistor with a resistance L*R is further needed to balance the negative temperature coefficient current, which causes the waste of large layout area. Therefore, there is a need to improve the prior art.